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Concept
Silicate
Summary
In chemistry, a silicate is any member of a family of polyatomic anions consisting of silicon and oxygen, usually with the general formula [SiO4−x(4-2x)− ]n, where 0 ≤ x < 2. The family includes orthosilicate (x = 0), metasilicate (x = 1), and pyrosilicate (x = 0.5, n = 2). The name is also used for any salt of such anions, such as sodium metasilicate; or any ester containing the corresponding chemical group, such as tetramethyl orthosilicate. The name "silicate" is sometimes extended to any anions containing silicon, even if they do not fit the general formula or contain other atoms besides oxygen; such as hexafluorosilicate .Most commonly, silicates are encountered as silicate minerals.
For diverse manufacturing, technological, and artistic needs, silicates are versatile materials, both natural (such as granite, gravel, and garnet) and artificial (such as Portland cement, ceramics, glass, and waterglass).
In all silicates, silicon atom occupies the center of an idealized tetrahedron whose corners are four oxygen atoms, connected to it by single covalent bonds according to the octet rule. The oxygen atoms, which bears some negative charge, link to other cations (Mn+). This Si-O-M-O-Si linkage is strong and rigid, which properties are manifested in the rock-like silicates. The silicates can be classified according to the length and crosslinking of the silicate anions.
Isolated orthosilicate anions have the formula SiO44−. A common mineral in this group is olivine ().
Two or more silicon atoms can share oxygen atoms in various ways, to form more complex anions, such as pyrosilicate Si2O76−.
With two shared oxides bound to each silicon, cyclic or polymeric structures can result. The cyclic metasilicate ring Si6O1812− is a hexamer of SiO32-. Polymeric silicate anions of can exist also as long chains.
In single-chain silicates, which are a type of inosilicate, tetrahedra link to form a chain by sharing two oxygen atoms each. A common mineral in this group is pyroxene.
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